In chromatographs such as a liquid chromatographic analyzer, a gas chromatographic analyzer or the like, a sample to be measured is let to pass through a column to be separated into components, and each of the separated components is detected as an output value at each elapsing time using a photometer such as a chromatographic detector.
Signals output from the chromatographic detector are recorded as time sequential data having a time interval of several hundreds ms. This is what is called a chromatogram having signal intensity in the ordinate and retention time in abscissa. In general, the signal intensity is converted to a digital value Ij every an arbitrary time interval (time tj) to execute data processing.
FIG. 3 shows an example of a chromatogram obtained by executing a body fluid amino acid analysis.
As shown in FIG. 3, peaks of 11 components from Gly (glycine) to Tyr (tyrosine) densely exist in the range of retention time from 23 to 34 (min). In such a case, area-quantitative calculation is conventionally executed using a vertically dividing method in which a vertical line is drawn from each minimum point between peaks, that is, what is called “a root”. However, this method produces an error as large as several tens % to cause an incorrect result when the peaks are strongly overlapped with each other. Therefore, when the chromatogram of such a kind needs to be quantitatively analyzed in a high accuracy, it has been general that the analyzing time is lengthened to improve the separation degree.
On the other hand, in order to perform quantitative calculation without lengthening the analyzing time even if peaks are overlapped so strongly with each other, quantitative calculation is tried to be performed using numerical analysis in a manner like data processing. This method is, for example, a non-linear least-square method.
In the case of using the non-linear least-square method, at least three independent parameters (A: area, TR: retention time, σ: standard deviation) are used as variables in order to execute fitting of a peak for one component. Therefore, in order to execute fitting of peaks for a plurality of components, it is necessary to calculate three parameters of Ai, TRi, σi for each of the components (i).
The conventional examples of using the non-linear least-square method are disclosed in Japanese Patent Application Laid-Open No. 6-324029 and Japanese Patent Application Laid-Open No. 63-151851.
These examples disclose that overlapping peaks on a chromatogram are curve-fit using a waveform function such as the Gaussian function or an EMG function (exponentially modified Gaussian function) which can express an asymmetric waveform of a peak. As shown in these examples, the overlapping peaks can be separated into individual peak waveforms, and the quantitative calculation can be performed by obtaining peak sizes such as a peak area and so on corresponding to a component of each of the peaks.